Process for calibrating an automatic transmission

ABSTRACT

A method is provided for calibrating an automatic transmission with a torque converter clutch. In order to avoid that the torque converter clutch still has capacity even if the pressure is commanded to be zero without modifying the behavior of the torque converter clutch behavior of all the production, the torque converter clutch minimum offset transmissions are detected and only on these transmissions the torque converter minimum clamp pressure is decreased by a pressure step and the torque converter clutch coast adapt reference cell is increased.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent Application No.08001886.4, filed Feb. 1, 2008, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The invention concerns a process for calibrating an automatictransmission with a torque converter clutch.

BACKGROUND

On some transmissions, the torque converter clutch (TCC) could stillhave capacity even though the pressure is commanded to 0 kPa, which isimpacting on the TCC behavior. This problem leads to a TCC chugglephenomenon at low torque (engine speed waving). It also degrades theperformance of the electronically commanded converter clutch(abbreviated EC3, which means that the torque converter clutch iscontrolled in order to regulate the torque converter) in coastconditions.

An existing calibration solution is a so-called TCC immediate off lowtorque feature which fixes the chuggle issue by releasing the TCC (offmode), but does not meet the customer expectations on coast EC3performance and therefore is insufficient.

Another approach is to re-adjust the calibration based on thetransmissions that have a minimum TCC offset. This solves coast EC3performance and chuggle problems on the transmissions with a minimum TCCoffset (marginal amount of the production), but damages the TCC behaviorof the “nominal offset” transmissions (majority of the production). Thetransmissions with a minimum TCC offset are those transmissions whoseTCC transmits some torque, even if the minimal pressure is commanded.

In EP 1 739 329 A2, a torque converter connecting an engine and atransmission of a vehicle is provided with a lockup clutch and acontroller is programmed to increase an engagement force of a lockupclutch under open loop control before shifting to feedback control onthe engaging force using a target slip rotation speed. When an enginetorque rapidly decreases during open loop control, the controllerdecreases the engaging force according to a variation amount of theengine output torque, thereby preventing an unintentional suddenengagement of the lockup clutch due to decrease in the engine outputtorque.

Document JP 2005291345 A describes a control device for an automatictransmission with an input torque detecting means for detecting inputtorque to a torque converter, a real differential pressure computingmeans for computing real differential pressure on the basis of the inputtorque when fastening of a lock-up clutch is concluded, a learning valuecomputing means for computing a difference between a differentialpressure command value and the real differential pressure when fasteningof the lock-up clutch is concluded as a learning value, and a learningvalue housing means for storing the learning value in relation to thedifferential pressure command value. A learning correcting meanscorrects the differential pressure command value by reading a learningvalue corresponding to the differential pressure command value from thelearning value housing means.

In view of the foregoing, at least one objective of the invention is toavoid that the torque converter clutch still has capacity even if thepressure is commanded to be zero without modifying the behavior of thetorque converter clutch behavior of all the production. In addition,other objectives, desirable features, and characteristics will becomeapparent from the subsequent summary and/or detailed description and theappended claims, taken in conjunction with the accompanying drawings andthis background.

SUMMARY

This at least one objective, other objectives, desirable features, andcharacteristics, are attained according to an embodiment of theinvention in that the torque converter clutch minimum offsettransmissions are detected and only on these transmissions the torqueconverter minimum clamp pressure is decreased by a pressure step and thetorque converter clutch coast adapt reference cell is increased.

The capacity learn feature according to the invention has been realizedon the basis of the following considerations: A torque converter clutch(TCC) minimum offset (“TCC min offset”) transmission is characterized bya high level of TCC apply pressure (actual TCC pressure) in anycondition for a given VBS pressure command. The torque converter clutchadapts will naturally learn down in order to lower the TCC applypressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 shows a schematical representation of an embodiment of theinvention.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit application and uses. Furthermore, there is nointention to be bound by any theory presented in the precedingbackground or summary or the following detailed description.

As can be seen from FIG. 1, in a first step the torque converter clutchminimum offset (TCC min offset) transmissions are detected. A torqueconverter clutch (TCC) minimum offset (“TCC min offset”) transmission ischaracterized by a high level of TCC apply pressure (actual TCCpressure) in any condition for a given VBS pressure command. The torqueconverter clutch adapts will naturally learn down in order to lower theTCC apply pressure.

Thus, the minimum offset is detected when a TCC coast adapt cell(designated by calibration) goes below the threshold P1threshold(calibrated value ˜10 kPa).

Then, if the calculated TCC pressure drops below P2threshold (calibratedvalue ˜2 kPa) in coast EC3 mode for a time greater than T2threshold(calibrated value ˜0.5 s) while the adapt is below the thresholdP1threshold (˜10 kPa), the TCC min clamp pressure is decreased by apressure step. In parallel, the TCC coast adapt reference cell is alsoreset to the pressure P1threshold+P3threshold (calibrated value+˜10kPa).

A TCC pressure conversion table (not represented) delivers the variablebleed solenoid (VBS) commanded pressure corresponding to a calculatedTCC pressure. The known table has been shifted and completed by a newarea for the lowest calculated pressures. As a consequence of theshifted table, the coast adapts cells values have been offset in orderto keep the same actual TCC pressure for a given calculated TCCpressure. This new extension can only be reached by decreasing the TCCmin clamp pressure (initially set at ˜20 kPa before learning).Consequently, if a “TCC min offset” transmission is detected, the TCCmin clamp pressure will decrease, and then will allow a lower VBSpressure command (new extension table area).

According to an embodiment of the invention, the TCC min clamp willremain at its initial value, so that there are no side effects of there-calibration of the “TCC min offset” transmissions on the rest of theproduction. Only “TCC min offset” transmissions will learn a lower TCCmin clamp pressure.

While at least one exemplary embodiment has been presented in theforegoing summary and detailed description, it should be appreciatedthat a vast number of variations exist. It should also be appreciatedthat the exemplary embodiment or exemplary embodiments are onlyexamples, and are not intended to limit the scope, applicability, orconfiguration in any way. Rather, the foregoing summary and detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment, it being understood thatvarious changes may be made in the function and arrangement of elementsdescribed in an exemplary embodiment without departing from the scope asset forth in the appended claims and their legal equivalents.

1. A method executed by a computer processor for calibrating anautomatic transmission with a torque converter clutch, the methodcomprising the steps of: detecting torque converter clutch minimumoffset transmissions when a torque converter clutch coast adapt celldecreases below a first pressure threshold; when the torque converterclutch minimum offset transmissions are detected and a calculated torqueconverter clutch pressure drops below a second pressure threshold for atime greater than a time threshold: generating a command to decrease aminimum clamp pressure applied to the torque converter clutch by apressure step; and generating a command to increase the torque converterclutch coast adapt reference cell to a new pressure.
 2. The methodaccording to claim 1, wherein the first pressure threshold is about 2kilopascals and the second pressure threshold is about two kilopascals,and wherein the time threshold is about one-half of a second.
 3. Themethod according to claim 1, wherein the torque converter clutch minimumoffset transmissions are characterized by a high level of actualy torqueconverter clutch apply pressure in any condition for a given variablebleed solenoid (VBS) pressure command.
 4. The method according to claim1, wherein the second pressure threshold is less than the first pressurethreshold in an electronically commanded converter clutch coast mode inwhich the torque converter clutch is controlled to regulate a torqueconverter in coast conditions.
 5. The method according to claim 1,wherein the new pressure is the sum of the first pressure threshold anda third pressure threshold.
 6. The method according to claim 1, whereinthe step of decreasing comprises: decreasing the torque converter clutchminimum clamp pressure by the pressure step if the torque converterclutch minimum offset transmissions are detected and the calculatedtorque converter clutch pressure drops below the second pressurethreshold for the time greater than the time threshold while the torqueconverter clutch coast adapt cell remains below the first pressurethreshold.